Grating coupler and preparation method and application thereof

Abstract

The invention provides a grating coupler and a preparation method and application thereof, and relates to the field of integrated photonics. The grating coupler structurally comprises a substrate layer, a silicon oxide lower cladding, a silicon nitride waveguide layer, a silicon oxide buffer layer, an amorphous silicon layer and a silicon oxide upper cladding from bottom to top, wherein the amorphous silicon layer comprises an amorphous silicon waveguide and an amorphous silicon grating from bottom to top, and the amorphous silicon grating is connected with the amorphous silicon waveguide; the amorphous silicon waveguide and the silicon nitride waveguide layer both comprise linear gradient waveguides which form a double-tapering structure, the double-tapering structure couples light from the silicon nitride waveguide layer into the amorphous silicon waveguide in a vertical coupling mode, and higher grating diffraction efficiency is achieved by means of the large refractive index difference between amorphous silicon and silicon dioxide. And the coupling efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the field of integrated photonics, and more specifically, to a grating coupler and a preparation method and application thereof. Background Art

[0002] In the context of the rapid development of informatization, optical communication and optical interconnection technologies have developed rapidly in terms of transmission distance and capacity. The resulting surge in global data volume has posed new challenges to data transmission and processing technologies. People are in urgent need of more efficient transmission and processing methods to meet the huge demand for data growth. Traditional multiplexing dimensions such as amplitude, wavelength, and polarization have gradually approached their performance limits. New multiplexing technologies based on space division and mode division of multi-core and multi-mode optical fibers have become a new means to improve the transmission capacity of the system. However, more complex problems such as distortion and crosstalk are introduced during the transmission process, which put forward higher performance requirements for signal processing units. Electronic devices face major challenges in processing massive amounts of data, mainly due to two core problems: first, the failure of Moore's Law has caused bottlenecks in the performance growth and energy efficiency improvement of electronic processors; second, although the clock frequency of electronic processors has reached the GHz level, even through parallel computing or architecture optimization, it is impossible to essentially bridge the huge gap between the processor operation rate and the data flow speed.

[0003] In this context, integrated photonic technology provides a solution that can achieve high-speed data processing and transmission. Integrated photonic technology uses photons as information carriers and completes complex information processing or data operations by building optical systems. It has the advantages of fast processing speed, low energy efficiency, anti-interference, compact structure, stability and low cost, providing a new solution to break through the current bottleneck of information data processing.

[0004] On the road to commercialization and maturity of photonic chip technology, a series of technical challenges need to be overcome. Among them, achieving efficient optical coupling between chip and optical fiber is particularly critical. At present, grating coupling technology has become the mainstream solution due to its design flexibility. Grating couplers can achieve optical signal coupling from optical fiber to chip, as well as reverse coupling, but they also face technical challenges such as coupling efficiency. Therefore, it is necessary to improve coupling efficiency. Summary of the invention

[0005] In view of the problem of low coupling efficiency in existing coupling devices, the present invention provides a grating coupler and a preparation method and application thereof to improve coupling performance.

[0006] In a first aspect, the present invention provides a grating coupler, comprising, from bottom to top, a substrate layer, a silicon oxide lower cladding layer, a silicon nitride waveguide layer, a silicon oxide buffer layer, an amorphous silicon layer, and a silicon oxide upper cladding layer;

[0007] Wherein, the amorphous silicon layer includes an amorphous silicon waveguide and an amorphous silicon grating from bottom to top;

[0008] The amorphous silicon waveguide and the silicon nitride waveguide layer both comprise a first straight waveguide, a linear gradient waveguide and a second straight waveguide connected in sequence, and the silicon nitride waveguide layer and the amorphous silicon waveguide form a double-tapered structure;

[0009] The amorphous silicon grating is located on the second straight waveguide of the amorphous silicon waveguide.

[0010] The silicon nitride waveguide layer and the amorphous silicon waveguide form a double-tapered structure, which couples the mode of the silicon nitride waveguide into the amorphous silicon waveguide in a vertical coupling manner and utilizes the large refractive index difference between amorphous silicon and silicon dioxide to achieve higher grating diffraction efficiency, thereby improving coupling efficiency.

[0011] In a preferred embodiment, the amorphous silicon grating is a non-periodic apodized grating structure, the depth of the etched position is 100-200 nanometers, and the duty cycle f of each unit of the grating varies linearly along the z direction and satisfies formulas (1) and (2).

[0012] f=f0-R·z (1)

[0013]

[0014] Where f0 is the duty cycle of the initial unit of the grating, in %;

[0015] R is the apodization coefficient, dimensionless;

[0016] z is the length along the z direction, in nm;

[0017] ∧ is the grating period, in nm;

[0018] λ is the wavelength of light; unit: nm;

[0019] n eff is the effective refractive index of light in the amorphous silicon grating, dimensionless;

[0020] θ is the diffraction angle in degrees.

[0021] By selecting the amorphous silicon grating as a non-periodic cut-toe grating structure, controlling the grating etching depth to a specific value and the period and duty cycle of each unit to satisfy the above formula, each unit of the grating coupler meets the Bragg diffraction condition and maximizes the coupling performance.

[0022] In a preferred embodiment, f0=0.95, θ=8°, and R=0.025.

[0023] In a preferred embodiment, the thickness of the silicon oxide upper cladding layer is 1.27 microns, the thickness of the silicon oxide buffer layer is 50 nanometers, and the thickness of the amorphous silicon layer is 260 nanometers. The thickness of the silicon oxide upper cladding layer is selected within the above range so that the diffracted light wave and the reflected light wave reach a constructive interference condition, further improving the diffraction efficiency.

[0024] In a preferred embodiment, the width of the amorphous silicon grating is 36 microns, and the length of the amorphous silicon waveguide is 125 microns.

[0025] In a preferred embodiment, the linear gradient waveguide of the amorphous silicon waveguide comprises a first end face and a second end face opposite to each other, and the width of the second end face is greater than the width of the first end face;

[0026] In the amorphous silicon waveguide, the width of the first straight waveguide is the same as the width of the first end surface and the first straight waveguide is connected to the first end surface, and the width of the second straight waveguide is the same as the width of the second end surface and the second straight waveguide is connected to the second end surface.

[0027] In a preferred embodiment, the width and height of the amorphous silicon waveguide and the end surface connecting the amorphous silicon grating are consistent.

[0028] In a preferred embodiment, the amorphous silicon grating includes an unetched portion of an amorphous silicon grating and an unetched portion of an amorphous silicon grating, and adjacent unetched portions of an amorphous silicon grating and an unetched portion of an amorphous silicon grating form an L-shape, and the unetched portion of an amorphous silicon grating and an unetched portion of an amorphous silicon grating have the same height.

[0029] In a preferred embodiment, the adapting coupling optical fiber of the grating coupler is a single-mode optical fiber, the input light source is a TE mode, and the operating band is a C band.

[0030] In a second aspect, the present invention provides a method for preparing the grating coupler, characterized in that it includes the following steps: depositing a silicon nitride film on a thermally oxidized silicon wafer, then making a silicon nitride waveguide on the silicon nitride film to form a silicon nitride waveguide layer, then depositing a silicon oxide buffer layer on the silicon nitride waveguide layer, then depositing an amorphous silicon layer on the silicon oxide buffer layer and making an amorphous silicon waveguide and an amorphous silicon grating, and finally depositing a silicon oxide upper cladding; the thermally oxidized silicon wafer includes a substrate layer and a silicon oxide lower cladding.

[0031] In a third aspect, the present invention provides an optical waveguide chip, comprising the grating coupler.

[0032] The present invention can bring the following positive effects:

[0033] (1) The present invention can improve the optical signal coupling efficiency from optical fiber to chip.

[0034] (2) The present invention is compatible with CMOS technology and can reduce production costs.

[0035] (3) The grating coupler structure of the present invention can be more flexibly integrated into different photonic chip designs to meet diverse application requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to fully understand the present invention and the significant advantages it brings, the following will be described in detail with reference to the attached figures, wherein:

[0037] Figure 1 is a longitudinal cross-sectional schematic diagram of a grating coupler according to an embodiment of the present invention;

[0038] Figure 2 A top view of an amorphous silicon layer in a grating coupler according to an embodiment of the present invention;

[0039] Figure 3 is a longitudinal cross-sectional schematic diagram of a grating unit in a grating coupler according to an embodiment of the present invention;

[0040] Figure 4 A top view of a silicon nitride-amorphous silicon composite layer in a grating coupler according to an embodiment of the present invention;

[0041] Figure 5 A specific application scenario of coupling a grating coupler and an external optical fiber according to an embodiment of the present invention;

[0042] Figure 6 The figure is a schematic diagram of a manufacturing process of a grating coupler according to an embodiment of the present invention.

[0043] [Description of Reference Numerals]

[0044] 101-substrate layer; 102-silicon oxide lower cladding; 103-silicon nitride waveguide layer; 104-silicon oxide buffer layer; 105-amorphous silicon layer; 1051-amorphous silicon waveguide; 1052-amorphous silicon grating; 1052a-unetched part of amorphous silicon grating; 1052b-etched part of amorphous silicon grating; 106-silicon oxide upper cladding; 107-optical fiber. DETAILED DESCRIPTION

[0045] The drawings are for illustrative purposes only and should not be construed as limiting the present patent;

[0046] In order to better illustrate the present embodiment, some parts in the drawings may be omitted, enlarged or reduced, and do not represent the size of the actual product;

[0047] It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0048] The present invention is described below in conjunction with the accompanying drawings and embodiments.

[0049] Example 1

[0050] This embodiment provides a grating coupler, whose structure is as follows Figures 1 to 4 shown.

[0051] Depend on Figure 1 It can be seen that the grating coupler includes, from bottom to top, a substrate layer 101, a silicon oxide lower cladding layer 102, a silicon nitride waveguide layer 103, a silicon oxide buffer layer 104, an amorphous silicon layer 105 and a silicon oxide upper cladding layer 106; wherein, the amorphous silicon layer 105 includes, from bottom to top, an amorphous silicon waveguide 1051 and an amorphous silicon grating 1052, and the amorphous silicon grating 1052 is connected to the amorphous silicon waveguide 1051; the amorphous silicon waveguide 1051 and the amorphous silicon grating 1052 are arranged between the silicon oxide buffer layer 104 and the silicon oxide upper cladding layer 106, and the silicon nitride waveguide 103, the amorphous silicon waveguide 1051 and the amorphous silicon grating 1052 together constitute a silicon nitride-amorphous silicon composite layer.

[0052] Depend on Figure 2 and 4 It can be seen that both the amorphous silicon waveguide 1051 and the silicon nitride waveguide layer 103 include a first straight waveguide, a linear gradient waveguide and a second straight waveguide, wherein the linear gradient waveguide of the amorphous silicon waveguide 1051 includes a first end face and a second end face opposite to each other, and the width of the second end face is greater than the width of the first end face; in the amorphous silicon waveguide 1051, the width of the first straight waveguide is the same as the width of the first end face and the first straight waveguide is connected to the first end face, the width of the second straight waveguide is the same as the width of the second end face and the second straight waveguide is connected to the second end face, and the amorphous silicon grating 1052 is located on the second straight waveguide of the amorphous silicon waveguide 1051. The amorphous silicon waveguide 1051 and the silicon nitride waveguide layer 103 form a double taper structure, which couples light from the silicon nitride waveguide layer 103 into the amorphous silicon waveguide 1051 in a vertical coupling manner, and uses the larger refractive index difference between amorphous silicon and silicon dioxide to achieve higher grating diffraction efficiency, thereby improving coupling efficiency. In addition, the amorphous silicon grating 1052 is a non-periodic apodized grating structure, the depth of the etched position is 160 nanometers, and the duty cycle f of each unit of the grating changes linearly along the z direction and satisfies formulas (1) and (2),

[0053] f=f0-R·z (1)

[0054]

[0055] Where f0 is the duty cycle of the initial unit of the grating, in %;

[0056] R is the apodization coefficient, dimensionless;

[0057] z is the length along the z direction, in nm;

[0058] ∧ is the grating period, in nm;

[0059] λ is the wavelength of light, in nm;

[0060] n eff is the effective refractive index of light in the amorphous silicon grating 1052, dimensionless;

[0061] θ is the diffraction angle, in degrees. By adjusting the etching depth of the grating and the period and duty cycle of each unit to satisfy the above formulas (1) and (2), each unit of the grating coupler meets the Bragg diffraction condition and maximizes the coupling efficiency. Where, f0 = 0.95, θ = 8°, R = 0.025.

[0062] The width of the amorphous silicon grating 1052 is 36 microns, the length of the amorphous silicon waveguide 1051 is 125 microns, and the width and height of the end surface connecting the amorphous silicon waveguide 1051 and the amorphous silicon grating 1052 are consistent.

[0063] Depend on Figure 3 It can be seen that the amorphous silicon grating 1052 includes an amorphous silicon grating unetched portion 1052a and an amorphous silicon grating unetched portion 1052b, and the adjacent amorphous silicon grating unetched portion 1052a and the amorphous silicon grating unetched portion 1052b form an L shape, so that the grating structure unit is L-shaped. The height of the amorphous silicon grating unetched portion 1052a and the amorphous silicon grating unetched portion 1052b is consistent. The specific number of grating structure units can be comprehensively considered according to the requirements of the technicians for the target device size and target performance.

[0064] The thickness of the silicon oxide upper cladding layer 106 is 1.27 microns, the thickness of the substrate layer 101 is 2 microns, the thickness of the silicon nitride waveguide layer 103 is 850 nanometers, the thickness of the silicon oxide buffer layer 104 is 50 nanometers, and the thickness of the amorphous silicon layer 105 is 260 nanometers. By preferably taking the above value for the thickness of the silicon oxide upper cladding layer 106, the diffracted light wave and the reflected light wave reach a constructive interference condition, further improving the diffraction efficiency. The thickness of each layer can be adjusted accordingly according to the actual application conditions to meet the actual needs.

[0065] according to Figure 5 The grating coupler of this embodiment is combined with the single-mode optical fiber 107 with a grinding angle of 8 degrees to realize the optical coupling between the chip and the external light source. When the input light source of the single-mode optical fiber 107 is TE mode and the working band is C band, the coupling loss is 3.87dB and the 3-dB bandwidth is 18 nanometers.

[0066] The preparation method of the grating coupler of this embodiment comprises the following steps: depositing a silicon nitride film on a thermally oxidized silicon wafer, then making a silicon nitride waveguide on the silicon nitride film to form a silicon nitride waveguide layer 103, then depositing a silicon oxide buffer layer 104 on the silicon nitride waveguide layer 103, then depositing an amorphous silicon layer 105 on the silicon oxide buffer layer 104 and making an amorphous silicon waveguide 1051 and an amorphous silicon grating 1052, and finally depositing a silicon oxide upper cladding layer 106; the thermally oxidized silicon wafer comprises a substrate layer 101 and a silicon oxide lower cladding layer 102.

[0067] Comparative Example 1

[0068] This comparative example provides a grating coupler, which is different from Example 1 in that the silicon nitride waveguide layer is a straight waveguide, the amorphous silicon waveguide is a straight waveguide, and the silicon nitride waveguide layer and the amorphous silicon waveguide do not form a double taper structure. The grating coupler of this comparative example is combined with a single-mode optical fiber 107 with a grinding angle of 8 degrees. When the input light source of the single-mode optical fiber 107 is a TE mode and the operating band is a C band, the coupling loss is 6.9 dB and the 3-dB bandwidth is 15 nanometers.

[0069] Comparative Example 2

[0070] This embodiment provides a grating coupler, which is different from the embodiment 1 in that the depth of the amorphous silicon grating etching position is 260 nanometers. The grating coupler of this embodiment is combined with a single-mode optical fiber 107 with a grinding angle of 8 degrees. When the input light source of the single-mode optical fiber 107 is TE mode and the working band is C band, the coupling loss is 5.87 dB and the 3-dB bandwidth is 18 nanometers.

[0071] Comparative Example 3

[0072] This embodiment provides a grating coupler, which is different from the embodiment 1 in that the grating duty cycle f is fixed to 0.52, rather than changing linearly along the z direction, that is, it does not satisfy formula (1). The grating coupler of this embodiment is combined with a single-mode optical fiber 107 with a grinding angle of 8 degrees. When the input light source of the single-mode optical fiber 107 is TE mode and the working band is C band, the coupling loss is 5.89 dB and the 3-dB bandwidth is 16 nanometers.

[0073] Comparative Example 4

[0074] This embodiment provides a grating coupler, which is different from the embodiment 1 in that the grating period Λ=1268nm, which does not satisfy formula (2). The grating coupler of this embodiment is combined with a single-mode optical fiber 107 with a grinding angle of 8 degrees. When the input light source of the single-mode optical fiber 107 is TE mode and the working band is C band, the coupling loss is 6.32dB and the 3-dB bandwidth is 18 nanometers.

[0075] Comparative Example 5

[0076] This embodiment provides a grating coupler, which is different from the embodiment 1 in that the thickness of the upper cladding layer of silica is 3 microns. The grating coupler of this embodiment is combined with a single-mode optical fiber 107 with a grinding angle of 8 degrees. When the input light source of the single-mode optical fiber 107 is TE mode and the working band is C band, the coupling loss is 5.43 dB and the 3-dB bandwidth is 18 nanometers.

[0077] The terms used in the drawings to describe positional relationships are only used for illustrative purposes and should not be construed as limiting this patent;

[0078] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A grating coupler, characterized in that: From bottom to top, it includes a substrate layer (101), a silicon oxide lower cladding layer (102), a silicon nitride waveguide layer (103), a silicon oxide buffer layer (104), an amorphous silicon layer (105) and a silicon oxide upper cladding layer (106); The amorphous silicon layer (105) comprises, from bottom to top, an amorphous silicon waveguide (1051) and an amorphous silicon grating (1052); the amorphous silicon waveguide (1051) and the silicon nitride waveguide layer (103) both comprise a first straight waveguide, a linear gradient waveguide and a second straight waveguide connected in sequence; the silicon nitride waveguide layer (103) and the amorphous silicon waveguide (1051) form a double taper structure; The amorphous silicon grating (1052) is located on the second straight waveguide of the amorphous silicon waveguide (1051).

2. The grating coupler according to claim 1, characterized in that: The amorphous silicon grating (1052) is a non-periodic apodized grating structure, the depth of the etched position is 100-200 nanometers, the duty cycle f of each unit of the grating changes linearly along the z direction and satisfies formulas (1) and (2), f=f0-R·z (1) Where f0 is the duty cycle of the initial unit of the grating, in %; R is the apodization coefficient, dimensionless; z is the length along the z direction, in nm; ∧ is the grating period, in nm; λ is the wavelength of light; unit: nm n eff is the effective refractive index of light in the amorphous silicon grating (1052), dimensionless; θ is the diffraction angle in degrees.

3. The grating coupler according to claim 1, characterized in that: The f0=0.95, the θ=8°, and the R=0.

025.

4. The grating coupler according to claim 1, characterized in that: The thickness of the silicon oxide upper cladding layer (106) is 1.27 micrometers, the thickness of the silicon oxide buffer layer (104) is 50 nanometers, and the thickness of the amorphous silicon layer (105) is 260 nanometers.

5. The grating coupler according to claim 1, characterized in that: The width of the amorphous silicon grating (1052) is 36 microns, and the length of the amorphous silicon waveguide (1051) is 125 microns.

6. The grating coupler according to claim 1, characterized in that: The linear gradient waveguide of the amorphous silicon waveguide (1051) comprises a first end face and a second end face opposite to each other, wherein the width of the second end face is greater than the width of the first end face; In the amorphous silicon waveguide (1051), the width of the first straight waveguide is the same as the width of the first end face and the first straight waveguide is connected to the first end face, and the width of the second straight waveguide is the same as the width of the second end face and the second straight waveguide is connected to the second end face; The width and height of the connecting end faces of the amorphous silicon waveguide (1051) and the amorphous silicon grating (1052) are consistent.

7. The grating coupler according to claim 1, characterized in that: The amorphous silicon grating (1052) comprises an amorphous silicon grating unetched portion (1052a) and an amorphous silicon grating unetched portion (1052b), and the adjacent amorphous silicon grating unetched portion (1052a) and the amorphous silicon grating unetched portion (1052b) form an L shape, and the heights of the amorphous silicon grating unetched portion (1052a) and the amorphous silicon grating unetched portion (1052b) are consistent.

8. The grating coupler according to claim 1, characterized in that: The matching coupling optical fiber of the grating coupler is a single-mode optical fiber, the input light source is a TE mode, and the working band is a C band.

9. The method for preparing a grating coupler according to any one of claims 1 to 8, characterized in that: The following steps are involved: A silicon nitride film is deposited on a thermally oxidized silicon wafer, and a silicon nitride waveguide is then fabricated on the silicon nitride film to form a silicon nitride waveguide layer (103). A silicon oxide buffer layer (104) is then deposited on the silicon nitride waveguide layer (103). Subsequently, an amorphous silicon layer (105) is deposited on the silicon oxide buffer layer (104) to fabricate an amorphous silicon waveguide (1051) and an amorphous silicon grating (1052). Finally, a silicon oxide upper cladding layer (106) is deposited. The thermally oxidized silicon wafer comprises a substrate layer (101) and a silicon oxide lower cladding layer (102).

10. An optical waveguide chip, characterized in that: It comprises the grating coupler as claimed in any one of claims 1 to 8.

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